1. Field of the Invention
The present invention is in the field of manufacturing ceramic materials having controlled acoustic properties by providing a predetermined pattern of internal voids in the ceramic using a photolithographic process.
2. Description of the Prior Art
It is known to employ piezo-electric ceramics for ultrasound transducers. The problem which exists is to couple the acoustic oscillatory energy of the transducer to the medium, for example, air or water, to efficiently transfer the energy for the propagation of the acoustic wave. Similar requirements occur for the operation of such a transducer as an ultrasound receiver.
The acoustic impedance of a material is dependent on the product of the speed of sound in the material and the density thereof. Both properties are characteristics of the material which can not controlled at least within broad limits. Although the density of a ceramic material can be controlled by introducing greater or lesser amounts of porosity into the structure, this can only be done at the expense of the stability of the material.
One solution which has been proposed is to provide a transducer composed of a piezo-electric ceramic which has an adaptation layer of material of lower density and a lower sound propagation velocity. Choosing an appropriate mean value for the ceramic material of the transducer and for the propagation medium can result in a very good adaptation, an optimum adaptation at one quarter wavelength, for this one wavelength alone.
Another solution which has been suggested is to fabricate the ceramic material of the ultrasound transducer in two phases to form a composite material. The one phase consists of the ceramic material matrix and the other is an additive which produces cavities in the ceramic material.